What is the theory for load test on dc compound generator?

Answer 1

Connect the circuit as per the circuit diagram shown in fig1. Keep the field regulator of the motor in the minimum resistance position and regulator of the generator in the maximum resistance position.2. Switch on the supply and start the motor with the help of its starter.3. Adjust the field regulator of the motor such that it runs its rated speed given on thename plate.4. Adjust the armature regulator of the generator to build up its rated voltage given on itsname plates on no load.5. Note down the no loads of ammeter and volt meter in tabular form.6. Increase the load gradually in steps and tabulate the readings7. Plot the external characteristics is load current Vs terminal voltage.8 Connect the generator for differentially compounding, repeat the process and plot theexternal characteristics.

Answer 2

Compound Generator CharacteristicsIn a compound generator, both series and shunt excitation are combined as shown in Fig. (3.13). The shunt winding can be connected either across the armature only (short-shunt connection S) or across armature plus series field (long-shunt connection G). The compound generator can be cumulatively compounded or differentially compounded generator. The latter is rarely used in practice. Therefore, we shall discuss the characteristics of cumulatively compounded generator. It may be noted that external characteristics of long and short shunt compound generators are almost identical.

External characteristic

Fig. (3.14) shows the external characteristics of a cumulatively compounded

generator. The series excitation aids the shunt excitation. The degree of compounding depends upon the increase in series excitation with the increase in load current.

(i) If series winding turns are so adjusted that with the increase in load current the terminal voltage increases, it is called over-compounded generator. In such a case, as the load current increases, the series field m.m.f. increases and tends to increase the flux and hence the generated voltage. The increase in generated voltage is greater than the IaRa drop so that instead of decreasing, the terminal voltage increases as shown by curve A in Fig. (3.14).

(ii) If series winding turns are so adjusted that with the increase in load

current, the terminal voltage substantially remains constant, it is called flat-compounded generator. The series winding of such a machine has lesser number of turns than the one in over-compounded machine and, therefore, does not increase the flux as much for a given load current. Consequently, the full-load voltage is nearly equal to the no-load voltage

as indicated by curve B in Fig (3.14).

(iii) If series field winding has lesser number of turns than for a flat compounded machine, the terminal voltage falls with increase in load

current as indicated by curve C m Fig. (3.14). Such a machine is called under-compounded generator